#include<iostream>
#include<cmath>
using namespace std;
int k, m, n;
int dp[40][40];
int main()
{
    cin >> k >> m >> n;
    if (k < n + m) {
        cout << 0 << endl;
        return 0;
    }
    dp[0][0] = 1;
    for (int i = 0; i <= m - 1; i++) {
        for (int j = 0; j <= n - 1; j++) {
            dp[i][j] += dp[i - 1][j];
            dp[i][j] += dp[i][j - 1];
        }
    }
    cout << dp[m - 1][n - 1] << endl;
    return 0;
}


